Variable capacity swash plate type compressors typically include a cylinder block provided with a number of cylinders, a piston disposed in each of the cylinders of the cylinder block, a rotatably supported drive shaft, and a swash plate. The swash plate is adapted to be rotated by the drive shaft. The rotation of the swash plate is effective to reciprocatively drive the pistons. The length of the stroke of the piston is varied by an inclination angle of the swash plate. The inclination angle of the swash plate is varied by controlling the pressure differential between a suction chamber and a crank chamber using a control valve means.
The control of the crank chamber pressure is critical to the performance and durability of the compressor. If the pressure differential between the suction chamber and the crank chamber is too high, certain components in the compressor will be susceptible to failure due to overrates. The pressure differential can also negatively affect the optimum operation of the compressor.
In the prior art, an electronic control valve has been used to control the flow from the crank chamber to the suction plenum. To protect the crank chamber from being over pressurized, the electronic control valve sensed inputs of the crank chamber pressure and suction chamber pressure. Over pressurization can have several undesirable consequences. The components of the compressor are designed to endure forces in a given direction. If the pressure within the crank chamber increases substantially, the forces acting on the various compressor components will reverse causing undesirable effects on the durability of parts such as the pistons and bearings. In addition, the compressor can remain fixed in the minimum capacity condition if the pressure differential is not controlled. Increased friction and decreased durability could also result if the compressor is operated continuously at high crank chamber pressures.
An object of the invention is to produce a swash plate type compressor wherein the pressure in the crank chamber is monitored.
Another object of the invention is to produce a swash plate type compressor wherein the pressure in the crank chamber is controlled to minimize friction and component stresses on the components of the compressor.
Another object of the invention is to produce a swash plate type compressor wherein the pressure in the crank chamber is controlled to result in increased durability and duty cycle of the compressor.
Still another object of the invention is to produce a swash plate type compressor wherein the pressure in the crank chamber is regulated to result in smoother operation of the compressor.